Lackies Said,

Just one of the weird legends Japan has. From Wikipedia: Kappa are sometimes said to take their victims for the purpose of drinking their blood, eating their livers or gaining power by taking their shirikodama (尻子玉?), a mythical ball said to contain their soul which is located inside the anus

Author Said,

puppygod Said,

I guess it comes with the immortality. You start to experiment, and it all goes downward slippery slope from there…

Speaking of substance abuse, it didn’t come up that much in the anime yet, but in the manga all the mermaids are depicted as heavy drinkers. Very heavy drinkers. As in “being washed ashore in Malaysia with epic hangover” is usual occurence for them. And hilarious running gag.